Hmmm... actually, Ramadan is one of the twelve months in the Islamic calendar (which is lunar, by the way.) It's the 9th month, and it's the same month that the Holy Qur'an was revealed to the Prophet Muhammad (peace be upon him) 14oo years ago.
During this month, Muslims fast during the day - from sunrise to sunset. They abstain from food, drink, relations with their spouses, any sin that they may constantly practice during the year, and other excessive things they do in their regular routines. Basically, it's a spiritual training period. If they can abstain from that which is lawful to them in regular days for this amount of time (like food, drink, relations with their spouses,) then they can abstain from the bad too! And if they can abstain from the bad during this time, it helps them really get rid of some of their major sins!
Not only that, it's good for the health - it's good for a person spiritually, mentally, physically and emotionally (and possibly financially too!) :)
And of course, it is one of the pillars of the Islamic religion for a Muslim to fast during the month of Ramadan. : ) It is obeying our Creator and Lord, Allah and that is our purpose in life. :)